Once you drop, you can’t stop – sometimes for up to 15 hours. Images revealing how LSD interacts with receptors in the brain could explain why a trip lasts so long, while another study involving a similar receptor unpicks how the drug makes these experiences feel meaningful. LSD acts on with a number of different receptors in the brain, including ones for the chemicals serotonin and dopamine, but it’s not known exactly which receptors are responsible for its various effects. Daniel Wacker and his colleagues at the University of North Carolina, Chapel Hill, used crystallography to look at the structure of LSD when it binds to a receptor in the brain that normally detects serotonin. They discovered that part of this serotonin 2B receptor acts as a lid, closing around the LSD molecule and trapping it. This could explain the extended trips the drug produces. “It takes LSD very long to get into the receptor, and once it’s stuck it doesn’t go away,” says Wacker.